The invention relates to an opto-electronic measuring device with spectrum coding.
With this type of device, parameters can be measured, such as the temperature, pressure, position of an object or of an element.
In a device of this type, a variation of the measured parameter introduces a variation of the travel difference in an interferometer adjusted to a dull tint and illuminated by a wide spectrum light source. The spectrum of the light flux at the output of the interferometer depends on the travel difference and so on the value of the measured parameter. Analysis of the spectrum of this flux gives access to the value of the parameter.
Numerous means have been proposed for carrying out such analysis; in particular, an article by Arditty, Bosselmann, Ulrich entitled "Multimode fiber coupled interferometric position sensor" (OPTO 1985, May 21-23, 1985, pp. 168-169), proposed using a MICHELSON interferometer to carry out this analysis. In this interferometer, also adjusted to a dull tint, measurement of the relative position of the mirrors, when the lateral contrast rise of the interferogram appears, corresponds to the introduction by this interferometer of a travel difference equal and of opposite sign to that introduced by the first interferometer. Thus, the travel difference is obtained and so the value of the parameter which it is desired to measure.
U.S. Pat. No. 4,867,565 to Lequime discloses an optical detection device including a sensor of the interferometric type having a birefringent active medium, which is subjected to the parameter to be measured. This sensor is linked by an optical fiber to a static optical demodulation system, essentially constituted by a set of birefringent elements placed between a polarizer and an analyzer.
This device is complex, suffers the drawbacks resulting from the use of polarized light, that can have only half of the power of an unpolarized source. Furthermore, birefringent elements have a high thermal dependence, that makes the device dependent of the temperature.
This device also faces problems of dispersion due to the strong wavelength dependence of the material birefringence.
U.S. Pat. No. 3,549,260 to Barringer discloses the use of a simple optical wedge to form interference of Fizeau fringes. It can be a wedge-shaped air space formed by a pair of thin transparent plates.